Circulichnis montanus Vialov, 1971

Circular to elliptical ring-like structure. The tunnel is 1–2 mm wide, uniform in a single specimen, and the diameter of the entire structure is 23–45 mm. Short branches tangential to the circular tunnel are present locally.

Diagnosis. Horizontal, cylindrical burrow, which shows a course along a regular circle or ellipse.

Remarks: The ichnogenus Circulichnus (the orthography as Circulichnis was addressed by Keighley and Pickerill, 1997).

Description Smooth, circular to slightly ellipsoidal traces. Burrow diameter 1.5-9 mm. Circle or ellipse diameter 43-53 mm. Preserved as positive hyporeliefs.

Remarks. Circulichnus is a monospecific facies-crossing ichnogenus that has been recorded not only in deep-marine faciès (e.g., McCann and Pickerill, 1988), but also in shallow-marine (e.g., Fillion and Pickerill, 1984) and nonmarine (Buatois and Mángano, 1993a) deposits. It ranges in age from the Ordovician (Fillion and Pickerill, 1984) to Paleocene (Ksiazkiewicz, 1977).

Circulichnis montan­us is a feeding structure (Fodinichnia) probably produced by vermiform animals.

This ichnotaxon has been recorded from deep-marine (e.g.,Pickerill and Keppie, 1981; McCann and Pickerill, 1988; Buatois et al., 1996a), shallow-marine (e.g., Fedonkin, 1988), mar­ginal marine (e.g., Fillion and Pickerill, 1990), and even nonmarine facies (Buatois and Mangano, 1993a). Therefore, Fillionand Pickerill (1984) regarded this form as a eurybathic ichno­taxon.

Description: Smooth, completely or incompletely preserved, elliptical traces preserved in positive hyporelief on the sole of
a 67 mm-thick slab of tool marked and current lineated mudstone/fine-grained sandstone interlayers. Geometry, orientation and ellipse size are variable, with a maximum (x) axis of 24 mm. Individual traces possess a fill of similar grain size to the lowermost preserving sandstone layer, are unlined, internally structureless and consistently 1.6 mm in observable diameter apart from areas where they have been partially exhumed by current activity. The possible smaller examples have been extensively eroded; as a result they cannot confidently be assigned to this ichnotaxon.